Climate Change Impacts on Canadian Agriculture

1. Climate Change Impacts on Canadian Agriculture R.F. Grant Dept. of Renewable Resources, Univ. of Alberta, Edmonton,Alberta

2. Climate Change Impacts - Positive • Higher concentrations of atmospheric CO2 (Ca) raise CO2 fixation rates and hence plant productivity • Doubled Ca raises plant growth by ~30% (C3) and ~10% (C4) • This rise is smaller if nutrients are limiting • Higher Ca lowers transpiration rates and hence water requirements • Doubled Ca lowers water requirements by ~15 - 25% • This reduction is larger if nutrients are limiting • Higher temperatures raise CO2 fixation rates, lengthen growing season • Plant productivity increases with mean annual temperature to 15oC • Higher temperatures accelerate mineralization, nutrient uptake

3. Climate Change Impacts - Negative • Higher temperatures raise evaporation rates and hence water requirements • 3.5oC increase raises water requirements by ~25%. • Offsets reduction in water requirements from higher Ca • more rapid soil drying during mid-continental summers can cause greater risk of agricultural drought, forest fires, and decreased quality and quantity of water in reservoirs. • However higher temperatures are also expected to cause higher precipitation (3.5oC rise in temperature  8-10% rise in precip.) • Precipitation may become more variable, which reduces productivity, increases erosion. • Effects of variable rainfall on productivity can be reduced by soil and water conservation practices that maintain SOM and improve WUE.

4. Climate Change Impacts - Negative • Higher temperatures raise respiration rates and hence C loss to atmosphere • Offsets C gain at mean annual temperatures greater than 15oC • More frequent heat waves over most land areas can cause heat stress in livestock and crops • Higher minimum temperatures allow expanded ranges for pests and diseases of humans, livestock and crops (e.g. grasshoppers, potato beetle).

5. Climate Change Impacts on Agricultural Geography during the 21st Century – Key points • Frost free season will be extended by ~40 days. • Growing seasons are already lengthening by 1 to 3 days per decade in northern regions • May need longer-maturing, heat-tolerant crop varieties • Seeding dates of annual crops will be ~3 weeks earlier • Regrowth of perennial crops will start 2-3 weels earlier and critical fall harvest dates will be 2-3 weeks later • Spring wheat will be replaced by winter wheat through most of the prairies • Corn may replace other cereals and soybean may replace canola through the southern and central prairies • Ponderosa pine may replace lodgepole pine in foothills forests.

6. Climate Change Impacts on Agricultural Productivity during the 21st Century – Key points • Average yields of canola and cereals in western Canada will increase from current levels by 10% to 30% by the end of the century • This increase will be larger in central and cooler regions (e.g. Peace River) and less in warmer regions (e.g. southern Saskatchewan) • The size of this increase depends upon the amounts by which temperature and precipitation rise • e.g. in southern Saskatchewan if temperature rises by 3oC and precipitation does not rise, then average yields will rise only marginally, but their variability will increase – insurance, storage. • But if temperature rises by 6oC and precipitation does not rise (worst case scenario), then average yields will decline and crop failure will become more frequent • Grassland productivity will increase by 20% to 25% • Changes in species composition (e.g. C3 to C4) may be an issue

7. Climate Change and Land Use in the 21st Century • Much of the increased agricultural productivity from climate change in N. America will be realized by northward expansion of cultivation • Possibly as much as 60Mha, depending on emission scenario • But northern soils are largely luvisolic, with fertility limitations to agriculture • This expansion will be offset by loss of cultivable area in most regions of Africa and in NE Brazil and Australia.